Linq表达式多个左外连接错误

Posted 2023-03-23

【中文标题】Linq表达式多个左外连接错误

【英文标题】：Linq expression multiple left outer join error

【发布时间】：2013-08-21 14:59:32

【问题描述】：

我无法执行以下 linq。

   var items(  from p in Patients 
    join q in MURWorksheets on p.PatientId equals q.PatientId into step1
    from s in step1.DefaultIfEmpty()
    join t in MURWorksheetAnswers on s.MURWorksheetId equals t.MURWorksheetId into step2


    from s2 in step2.DefaultIfEmpty()

    select new p.FirstName , Date = (s.MURDate == null ? DateTime.Now.Date : s.MURDate),
    s2.MURQuestionnaireId,s2.MURExpctedAnswersId).ToList();

这是相同的sql供您参考。

select a.FirstName,b.MURDate,c.MURQuestionnaireId,c.MURWorksheetAnswersID from Patients as a
left join MURWorksheet as b on a.PatientId = b.PatientId
left join MURWorksheetAnswers as c on b.MURWorksheetId = c.MURWorksheetId

【问题讨论】：

有错误提示吗？

是的，使用 LinqPad ; expected Invalid expression term 'in'

那里是否有两个错误“;预期”和“无效的表达式术语'in'”？您可以编辑问题并在课堂上包含代码吗？

我假设您的代码是“var items = ...”而不是“var items(...”？

感谢 GrandMasterFlush，如果您在答案中发帖，您可能会获得积分。非常感谢，你回答 camse 1st

【参考方案1】：

您在粘贴的代码中缺少等号：

var items = (from p in Patients 
    join q in MURWorksheets on p.PatientId equals q.PatientId into step1
    from s in step1.DefaultIfEmpty()
    join t in MURWorksheetAnswers on s.MURWorksheetId equals t.MURWorksheetId into step2


    from s2 in step2.DefaultIfEmpty()

    select new p.FirstName , Date = (s.MURDate == null ? DateTime.Now.Date : s.MURDate),
    s2.MURQuestionnaireId,s2.MURExpctedAnswersId).ToList();